This invention relates generally to methods for the manufacture of solid surface articles such as countertops, sinks, backsplashes and the like. More specifically, the invention relates to methods and materials for a mold based process for the manufacture of high quality solid surface articles which are resistant to moisture and simulative of stone.
Countertops, sinks, tables, sills and the like have long been manufactured from marble, granite and other such natural stone; however, natural stone is expensive, difficult to fabricate, heavy, and very prone to breakage and staining. Hence, a number of synthetic materials simulative of stone have been employed for these purposes. Such materials are based upon organic polymers used either alone or in combination with fillers and particulates comprised of natural stone, man-made materials and various combinations. Very often, such synthetic materials are fabricated utilizing curable resins which can be cast or sprayed into place and which subsequently harden to produce a simulated stone article.
One class of simulated stone materials comprises those known in the art as xe2x80x9ccultured marble.xe2x80x9d Such cultured marble articles have an exterior surface comprised of a polymeric gel coat, which is typically a relatively transparent, relatively thin layer of cured polymeric resin which covers a thicker body of opaque polymeric resin which contains pigments, mineral particles, fillers and the like, and which is generally non-homogeneous so as to simulate the veining and color variations of natural stone. The durability of cultured marble is relatively low, owing to the generally low cut and abrasion resistance of the exterior gel coat. Also, moisture resistance of the gel coat is not very great, and hence moisture-caused delamination can occur. Nonetheless, cultured marble is relatively low in cost and is widely utilized.
Another class of synthetic surface materials comprises solid surface materials. These materials do not include a gel coat but have an exterior surface typically comprised of a relatively durable polymer based material which typically comprises a fairly opaque polymeric body loaded with relatively high levels of a high strength filler such as alumina trihydrate or the like, together with particulate inclusions. The particles may comprise a solid polymer, a mineral material or a composite of polymer and mineral. The particulate inclusions typically are visually distinct from the base polymer and provide the material with the appearance of stone. Solid surface materials are relatively hard, and since they do not include an exterior gel coat, scratches, chips and the like may be removed by polishing the material to expose a fresh surface. Solid surface materials are typically fabricated from a curable polymeric resin having fillers and particulate material therein. Solid surface coatings are generally applied to a support substrate which may comprise another body of polymer, wood, metal or the like. Such coatings are typically applied by spraying, and are generally then polished to provide a finished surface. Solid surface materials are relatively expensive, with costs being roughly equivalent to that of natural stone.
U.S. Pat. No. 5,476,895 discloses a solid surface coating simulative of granite. This coating is fabricated from polymeric resin which includes therein particulate granules which are composites of thermoplastic and thermoset polymers. Fabrication of this coating requires that the particulate inclusions be isopycnic with the resin, that is to say the particles must be neutrally buoyant in the resin. Isopycnicity is required in order to prevent the particles from stratifying in the coating as it cures, thereby destroying the stone-like appearance of the material.
Another solid surface coating is disclosed in U.S. Pat. No. 5,789,032. This coating is based upon a thermoset resin, and is applied to a solid support such as particleboard. U.S. Pat. No. 4,544,584 discloses a synthetic stone article fabricated from a curable organic resin having particulate matter dispersed therein so as to be simulative of onyx.
Prior art simulated stone materials are generally expensive to fabricate and often have poor moisture resistance. Therefore, such materials are less than satisfactory for many applications. There is thus a need for materials and methods whereby solid surface, simulated stone articles may be readily fabricated by low cost, easy to implement processes. Furthermore, the resultant article should be high in hardness and resistant to moisture. As will be explained in detail hereinbelow, the present invention is directed to methods and materials for the fabrication of high quality solid surface materials. These and other advantages of the present invention will be apparent from the drawings, discussion and description which follow.
There is disclosed herein a method for the manufacture of a solid surface article. The method includes the steps of providing a mold having a mold cavity defined therein, which cavity corresponds to the article being fabricated. A curable coating composition is provided. This composition includes at least 25% by weight of a liquid, thermosetting resin; 25-40% by weight of a polymerizable vinyl material; 0.1-10% by weight of an air release agent; 0.1-10% by weight of a wetting agent; and a thixotropic agent present in an amount sufficient to provide the composition with a thixotropic index of at least 4.5. The curable coating composition further includes 10-40% by volume of a solid, particulate material having a particle size of up to 0.1 inch therein. This curable composition is coated onto at least a portion of the mold cavity and allowed to cure so as to form the article. In some instances, a first layer of the curable composition is applied to the mold and at least partially cured, and then a curable body of backer material is disposed upon the layer of at least partially cured material.
In particular embodiments, the thermoset resin comprises a neopentylglycol isophthalate resin. The composition may further include mineral fillers, coupling agents, coloring agents, ultraviolet stabilizers and the like. The present invention avoids the needs for using isopycnic particles in the composition, and in some instances, the preferred particles are negatively buoyant.
Also disclosed herein is a fabrication process wherein a first coat of solid surface material is applied to a mold and at least partially cured, and a compression molding process is employed to conform a body of at least semi-solid backing material onto the solid surface material.